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Multicast Commands 1149
User Guidelines
Use of a multicast routing protocol is recommended (e.g., PIM, when ip
multicast is enabled).
Unless required, IGMP/MLD snooping should be disabled when ip multicast
is enabled. If a multicast source is connected to a VLAN on which both L3
multicast and IGMP/MLD snooping are enabled, the multicast source is
forwarded to the mrouter ports that have been discovered when the multicast
source is first seen. If a new mrouter is later discovered on a different port, the
multicast source data is not forwarded to the new port. Likewise, if an existing
mrouter times out or stops querying, the multicast source data continues to
be forwarded to that port. If a host in the VLAN subsequently joins or leaves
the group, the list of mrouter ports is updated for the multicast source and
the forwarding of the multicast source is adjusted. The workaround to this
limitation is to statically configure mrouter ports when enabling IGMP/MLD
snooping in L3 multicast enabled VLANs.
Example
The following example enables IP multicast on the router.
console#configure
console(config)#ip multicast
console(config)#ip igmp
ip multicast ttl-threshold
Use the ip multicast ttl-threshold command in Interface Configuration
mode to apply a
ttlvalue
to a routing interface.
ttlvalue
is the TTL threshold
which is applied to the multicast Data packets forwarded through the
interface.
Syntax
ip multicast ttl-threshold
ttlvalue
no ip multicast ttl-threshold
•
ttlvalue
— Specifies TTL threshold. (Range: 0-255)
2CSPC4.X8100-SWUM102.book Page 1149 Friday, March 15, 2013 8:56 AM